Precision bores such as for engine cylinders, fuel injectors, bearing bores, and gear bores are typically produced by the steps of: 1) boring or drilling to produce an initial bore; 2) reaming, boring, grinding or honing the bore with conventional tooling to enlarge and finish the hole, thus providing accurate dimensions and improving the finish of the bore walls; and 3) superfinishing the bore to smooth the surface of the bore.
The term "superfinishing" is herein used in reference to lapping, deburring, polishing, or other operations in which substantially improved surface characteristics are achieved. Machine tools for superfinishing are known in the art which have means for adjusting inserted blades or stones such that a definite size can be maintained through numerous cuttings and grindings and used-up blades can be replaced with new ones. U.S. Pat. No. 2,472,554 discloses an expandable reamer comprising a hollow cylinder and a shank axially extending therefrom, the cylinder having a plurality of radially disposed slots in its wall, each retaining a radially disposed blade extending therefrom.
Adjustable reamers are also known which are expandable such as by means of a wedge or tapered cone internal to the cylindrical cutting tool. U.S. Pat. No. 3,526,057 describes an axially tapered lap holding part which is capable of radially expanding or contracting. The lap holding part includes means for axially retaining a lap which is capable of radially expanding or contracting with the lap holding part, means for moving an axially tapered arbor with respect to the axial taper on the lap holding part to radially expand or contract the lap holding part, and means for maintaining the lap holding part axially stationary during its radial expansion or contraction so that the lap radially expands or contracts with the lap holding part without changing the relative axial position of the lap with respect to the workpiece that the lap is abrading.
U.S. Pat. No. 5,022,196 discloses a radially adjustable honing tool mountable for rotation on a honing machine comprising an elongated tubular cutting member having a slit extending lengthwise along its entire length and inner and outer surfaces wherein the inner surface is conically tapered over substantially the length thereof. The tool further comprises an elongated expander member positioned extending through the tubular member, having an outer surface tapered for making surface-to-surface contact with the tapered inner surface of the tubular member wherein the expander member is axially movable within the tubular member to change the diameter thereof uniformly along its length such that axial movement of the extender changes the diameter of the tubular cutting member.
Adjustable reamers and cutting tools such as those described above are complex and expensive and may provide more precision with respect to bore diameters than is necessary for a finishing step. Accordingly, there remains a need in the art for simple, inexpensive machine tools for superfinishing of bores.
Another problem with available prior art superfinishing equipment is that it provides surface bearing ratios generally in the range of 0.5% to 10%. No inexpensive superfinishing equipment is known which consistently provides surface bearing ratios greater than 10%.